Using the Multifunction Advanced Data Link, stealthy F-35s like these would be able to communicate with each other without sacrificing stealth. (Lockheed Martin)

WASHINGTON — Pentagon officials have long identified the F-35 joint strike fighter as key to the future of America’s defense, in large part due to stealth capabilities that should allow the plane to travel in contested environments that older fighters would struggle to penetrate.

The problem is, these planes need to talk to each other without sacrificing stealth. To tackle that problem, the F-35 has incorporated Northrop Grumman’s Multifunction Advanced Data Link (MADL), a system that’s undergoing testing in the California desert.

MADL is a digital waveform designed for secure transmission of voice and data between F-35s, with the potential of linking F-35s to ground stations or other aircraft, Northrop said.

Think of the system as a computer. The communications, navigation and identification (CNI) system on an F-35 can manage 27 different waveforms, including MADL. The data comes through the antenna, is turned into digitized bits, and is crunched by the on-board systems to get the relevant information to the pilots.

The system will be included in the 2B software package that the US Marine Corps’ F-35B jump-jet variant and the US Air Force’s F-35A conventional version will use when they reach initial operating capability in 2015 and 2016, respectively. It also will be included in all international versions of the jet. The US Navy’s F-35C carrier variant is expected to reach IOC in 2019 with the block 3F software, which will incorporate MADL and other capabilities.

What makes MADL more than just a communications tool is its ability to connect with other planes and automatically share situational awareness data between fighters. The more planes in the network the greater the data shared and the more comprehensive a picture is formed.

Picture a group of jets flying in formation. The pilot farthest to the right will have a different situational awareness picture than the pilot on the left. But once they’re networked, all the information is automatically shared among the pilots.

Prior to takeoff, planes would be designated with partners to form the network. When a plane gets within range, the network is automatically created.

“Like on your computer, your network into the local area, we’re building that network in the sky and it’s keeping up with all the dynamics and spatial changes,” said Bob Gough, director of CNI technology and programs at Northrop. “MADL has the smarts to keep up with all of that and keep the network in place so they can share the same data.”

Gough declined to say how close jets need to be to trigger the network link, but did say tests have shown “very fast” acquisition times once within range.

Live flight system tests at Edwards Air Force Base, Calif., began late last year and have continued throughout this year. Initially, the tests involved networking a pair of planes, but recently, test pilots began regularly flying four-plane networks. Those tests are proceeding smoothly, said Joe DellaVedova, a spokesman for the Pentagon’s F-35 Joint Program Office.

“MADL testing is performing as planned,” DellaVedova wrote in an email. “Development of the advanced data link is currently tracking to deliver the phased capability expected by the end of development.”

The system is designed for plane-to-plane communications only, something Gough expects to continue in the near term. But he did not rule out experimenting with data transfer to other terminals.

“We have postulated MADL terminals on ships and we have built a MADL test ground station, so it could be done,” he said. “But it’s more about the logistics of where F-35s will be flying and how close to the ground they would be. It would be mission-scenario dependent, but it’s all technically possible.”

In the long term, Northrop hopes to expand the technology to other fifth-generation planes. That’s not a new idea; in 2008, MADL was slated to go on the F-22 Raptor fighter and B-2 bomber. But it never went on those jets, something the former Air Force chief of staff, Gen. Norton Schwartz, blamed on the technology’s lack of maturity during congressional testimony in 2009.

“We believe as the flight test program matures, it will be more likely” to end up on other platforms, Gough said.

That could include using MADL to communicate between fifth-generation fighters like the JSF and fourth-generation fighters, such as an F-16. Gough said he hopes to begin research on fifth-to-fourth generation data transfers “as soon as” next year.